Métodos espectroscópicos de análise (2014) QFL-4030 Métodos espectroscópicos de análise (2014) Home Page: http://www2.iq.usp.br/docente/majokato (courses)

2nd ed. Saunders College Publishing. Literatura Silverstein, R. M., Webster, F. X. and Kiemle, D. J. (2005) Spectrometric identification of organic compounds, 7th ed. J. Wiley & Sons. Pavia, D. L., Lampman, G. M., Kriz, G. S. (1996). Introduction to spectroscopy. 2nd ed. Saunders College Publishing. Modern Instrumental Techniques for Schools and Colleges Royal Society of Chemistry – Advancing the Chemical Sciences: https://www.youtube.com/watch?v=DDTIJgIh86E

Objetivos Apresentar os fundamentos básicos e as aplicações dos principais métodos espectroscópicos utilizados em análise química estrutural, de modo a capacitar os alunos a interpretar espectros.

Programa Espectroscopia no UV-vis, infravermelho (IV), espectrometria de massas e ressonância magnética nuclear.

Quinina: Pelletier e Magendie, 1820 Atropina: Mein, 1831. Discovery of organic compounds was primarily motivated by bioactivity and their structural determination was based mostly on degradative reactions Morfina: Sertürner, 1805 Quinina: Pelletier e Magendie, 1820 Atropina: Mein, 1831. Papaverina: Merck, 1848. Cocaína: Wöhler, 1859. Escopolamina: Landenburg, 1881. Efedrina: Nagai, 1885. Tubocurarina: Boehm , 1895. Insulina: Abel, 1929.

Penicilina: Fleming, 1929. Dicumarol: Link, 1941. Cloranfenicol: Burkholder, 1947. Reserpina: Müller, 1952. Prostaglandinas: Bergströn, 1962. Encefalinas: Hughes, 1975.

Uso como antimalárico: Desde 1638 Isolamento: 1820 por Pelletier e Caventou Síntese: 1944 por Woodward

Determinação estrutural da quinina por reações de degradação

Confirmadas por síntese dos fragmentos obtidos

Quinine (natural antimalarial compound) Synthetic derivatives: Cinchona officinalis (quinine bark - Rubiaceae) Synthetic derivatives: Mefloquine (Lariam, Mefaquin) This quinine analog developed at Walter Reed Army Institute of Research (USA) and was used for the prophylaxis of malaria and also for treatment of chloroquine-resistant falciparum type. Primaquine Is used to treat malaria caused by P. vivax and P. ovale. It should be used in association with chloroquine or mefloquine to provide a complete cure. It is also used to treat fungal infections caused by Pneumocystis pneumonia, common in patients with AIDS.

Composição (tipos e quantidade de átomos): AE Rotação: Micro-ondas Como diferenciar uma molécula de outra? Ponto de fusão, índice de refração, forma, tamanho, etc… Massa: EM Composição (tipos e quantidade de átomos): AE Rotação: Micro-ondas Vibração: Infravermelho Orbitais moleculares: UV-Vis Organização em cristais: Difração de raios X Estados de spin (mediante campo magnético): RMN

Análise elementar – Determinação fórmula mínima CxHyOz + O2 (excesso) = x CO2 + y/2 H2O 9.83 mg 23.26 mg 9.52 mg Fórmula mínima CxHyOz, x = 64.6%; y = 10.8%; z = 24.6% C7H14O2

Vibrational transitions Bond breaking Eletronic transitions Nuclear spin transitions energy EM UV-VIS IV RMN frequency

Comparação do comprimento de onda http://upload.wikimedia.org/wikipedia/commons/thumb/d/d9/Espectro_Eletromagn%C3%A9tico.png/700px-Espectro_Eletromagn%C3%A9tico.png

General scheme for structural elucidation of natural compounds

CxHyOz C4H6O MM = 70 u.a. CC C-H OH C-O C-H CH2 OH CH2 CH -18 (OH) 𝐼=𝐶 − 𝐻 2 − 𝑋 2 + 𝑁 2 +1=2 CC C-H OH C-O C-H CH2 OH CH2 CH

Análise funcional orgânica Determinação de grupos funcionais: Análise funcional orgânica Espectrofotometria no Ultravioleta e infravermelho

Infrared radiation λ = 2.5 to 17 μm n (número de onda) = 4000 to 600 cm-1 These frequencies match the frequencies of covalent bond stretching and bending vibrations. Infrared spectroscopy can be used to find out about covalent bonds in molecules. IR is used to tell: 1. what type of bonds are present 2. some structural information

Infrared n Converted in Vibrational energy in molecules Depends on: 10,000 cm-1 to 100 cm-1 Converted in Vibrational energy in molecules Vibrational Spectra appears as bands instead of sharp lines => as it is accompanied by a number of rotational changes Wave Number => n (cm-1) => proportional to energy Older system uses the wavelenght l (mm => 10-6 m) cm-1 = 104 / mm n Depends on: Relative masses of atoms Force constant of bonds Geometry of atoms

Lei de Hooke

Instrumentação

IR source è sample è prism è detector   graph of % transmission vs. frequency => IR spectrum 100 %T 4000 3000 2000 1500 1000 500 v (cm-1)

Intensity in IR Intensity: Transmittance (T) or %T T = I I0 Absorbance (A) A = log I I0 IR : Plot of %IR that passes through a sample (transmittance) vs Wavelenght

Instrumentação

Espectro no IV

Infrared Position, Intensity and Shape of bands gives clues on Structure of molecules Modern IR uses Michelson Interferometer => involves computer, and Fourier Transform (FTIR) Sampling => plates, polished windows, Films … Must be transparent in IR NaCl, KCl : Cheap, easy to polish NaCl transparent to 4000 - 650 cm-1 KCl transparent to 4000 - 500 cm-1 KBr transparent to 400 cm-1

Infrared: Low frequency spectra of window materials Transmission of different window materials: CsI, CsBr, KBr, NaCl, CaF2 and Ge; Thickness: Ge 3 mm, CsBr 4mm, all others 5mm How to prepare samples IR Spectroscopy and how to take an IR spectrum. https://www.youtube.com/watch?v=FfI5BczOXQ8

IR-Absorption by Solvents Most solvents are of little use for IR spectroscopy because they block most of the of the typical spectral range range (4000 - 600 cm-1). A few notable exceptions are CS2, CHCl3 and CCl4 A complete solution spectrum of a compound can usually be assembled by measuring in CS2 and CHCl3.

CCl4

http://fy. chalmers. se/OLDUSERS/brodin/MolecularMotions/CCl4modes http://fy.chalmers.se/OLDUSERS/brodin/MolecularMotions/CCl4modes.html

Vibrations Stretching frequency Bending frequency O H C C—H www.cem.msu.edu/~reusch/Virtual/Text/Spectrpy/InfraRed/infrared.htm Vibrations Stretching frequency Bending frequency C O H Modes of vibration Bending Stretching C—H Wagging 1350 cm-1 Scissoring 1450 cm-1 Symmetrical 2853 cm-1 Rocking 720 cm-1 Asymmetrical 2926 cm-1 Twisting 1250 cm-1

Modos vibracionais http://chemwiki.ucdavis.edu/Physical_Chemistry/Spectroscopy/Vibrational_Spectroscopy/Vibrational_Modes

Vibrations General trends: www.cem.msu.edu/~reusch/Virtual/Text/Spectrpy/InfraRed/infrared.htm Vibrations General trends: Stretching frequencies are higher than bending frequencies (it is easier to bend a bond than stretching or compresing them) Bond involving Hydrogen are higher in freq. than with heavier atoms Triple bond have higher freq than double bond which has higher freq than single bond

Symmetrical and asymmetrical stretch Methyl 2872 cm-1 2962 cm-1 O O 1760 cm-1 1800 cm-1 Anhydride —N H —N H Amino 3300 cm-1 3400 cm-1 —N O —N O Nitro 1350 cm-1 1550 cm-1

Estiramentos Ou deformações axiais

IR spectra of ALKANES C—H bond “saturated” (sp3) 2850-2960 cm-1 -CH3 + “ and 1375 -CH(CH3)2 + “ and 1370, 1385 -C(CH3)3 + “ and 1370(s), 1395 (m)

n-pentane 2850-2960 cm-1 CH3CH2CH2CH2CH3 sat’d C-H 3000 cm-1

n-hexane CH3CH2CH2CH2CH2CH3

cyclohexane no 1375 cm-1 no –CH3

IR of ALKENES =C—H bond, “unsaturated” vinyl (sp2) 3020-3080 cm-1 + 675-1000 RCH=CH2 + 910-920 & 990-1000 R2C=CH2 + 880-900 cis-RCH=CHR + 675-730 (v) trans-RCH=CHR + 965-975 C=C bond 1640-1680 cm-1 (v)

Bond length and strength vs Stretching frequency

1-decene 3020-3080 cm-1 C=C 1640-1680 unsat’d C-H 910-920 & 990-1000 RCH=CH2 C=C 1640-1680

Alkene In large molecule local symmetry produce weak or absent vibration R trans C=C isomer -> weak in IR C=C R Observable in Raman

cis-4-octene 1665

trans-4-octene 1665

2055 cm-1

Nitrile

Other Nitrogen Compounds Nitriles R-CN : Sharp 2250 cm-1 Conjugation moves to lower frequency Isocyanates R-N=C=O Broad ~ 2270 cm-1 Isothiocyanates R-N=C=S 2 Broad peaks ~ 2125 cm-1 Imines / Oximes R 2C=N-R 1690 - 1640 cm-1

Como as bandas no IV são afetadas? Eletronegatividade do carbono (C-H) Números de onda Maiores/ Frequencias maiores 3300 cm-1 3100 cm-1 2900 cm-1

styrene no sat’d C-H 1640 C=C 910-920 & 990-1000 RCH=CH2 mono

Infrared of alcohols and amines O–H 3400 to 3650 cm1 Usually broad and intense N–H 3300 to 3500 cm1 Sharper and less intense than an O–H

Cyclohexanol

IR spectra ALCOHOLS & ETHERS C—O bond 1050-1275 (b) cm-1 1o ROH 1050 2o ROH 1100 3o ROH 1150 ethers 1060-1150 O—H bond 3200-3640 (b) 

1-butanol 3200-3640 (b) O-H C-O 1o CH3CH2CH2CH2-OH

2-butanol O-H C-O 2o

tert-butyl alcohol O-H C-O 3o

methyl n-propyl ether no O--H C-O ether

Free OH and Hydrogen bonded OH

Band Shape: OH vs NH2 vs CH

Infravermelho de aminas

Estiramento de compostos carbonílicos

Which compound is this? 2-pentanone 1-pentanol 1-bromopentane 2-methylpentane 1-pentanol

What is the compound? 1-bromopentane 1-pentanol 2-pentanone 2-methylpentane 2-pentanone

Ketone and Conjugation Conjugation: Lower

n Ketone and Ring Strain Factors influencing C=O 2) Ring size 1715 cm-1 1751 cm-1 1775 cm-1 Angle ~ 120o < 120o << 120o n Ring Strain: Higher

Factors influencing carbonyl: C=O 3) a substitution effect (Chlorine or other halogens) —C—C— X O n Result in stronger bound  higher frequency 1750 cm-1 4) Hydrogen bonding Decrease C=O strenghtlower frequency 1680 cm-1

Factors influencing carbonyl: C=O 5) Heteroatom Inductive effect Resonance effect Weaker bond Lower frequence Stronger bond higher frequency e.g. ester e.g. amides Y C=O Cl 1815-1785 Br 1812 inductive OH (monomer) 1760 OR (Ester) 1705-1735 NH2 1695-1650 resonance SR 1720-1690

n n n Ester Carbonyl Esters C=O ~ 1750 – 1735 cm-1 Conjugation => lower freq. O-C : 1300 – 1000 2 or more bands Inductive effect with O reinforce carbonyl => higher n Conjugation with CO weaken carbonyl => Lower n

Ester carbonyl: C=O

Lactone carbonyl: C=O Lactones  Cyclic Ester 1720 1735 1760 1750 1770 1800

Carbonyl compounds : Acids Carboxylic acid Exist as dimer : Strong Hydrogen bond OH : Very broad  3400 – 2400 cm-1 C=O : broad  1730 – 1700 cm-1 C—O : 1320 – 1210 cm-1 Medium intensity

Carbonyl compounds : Acids OH C=O C=O : 1711 cm-1 OH : Very Broad 3300 to 2500 cm-1 C-O : 1285, 1207 cm-1

Anhydrides C=O always has 2 bands: 1830-1800 and 1775-1740 cm-1 C—O multiple bands 1300 – 900 cm-1

Carbonyl compounds : Aldehydes ~ 1725 cm-1 Conjugation => lower freq. O=C-H : 2 weak bands 2750, 2850 cm-1 C=O : 1724 cm-1

Carbonyl compounds : Aldehydes

IR SPECTRA: WHAT YOU CAN TELL AT A GLANCE Is carbonyl group present (1820-1650 cm-1)? Acid OH: 3400-2400 cm-1 Amides N-H: 3400 cm-1 Ester C-O: 1300-1000 cm-1 Anhydrides two bands: 1810 and 1760 cm-1 Aldehydes C-H: 2850 and 2750 cm-1 Ketones preceding 5 choices eliminated

2) If C=O is absent: ROH OH: 3400-3300 cm-1; or ArOH C-O near 1300-1000 cm-1 Amines N-H: 3400 cm-1) Ether C-O: 1300-1000 cm-1; absence of OH Double bond/aromatic ring: C=C: weak band near 1650 cm-1; 1600-1450cm-1)

Triple bonds C=N: 2250 cm-1 (m) C=C: 2150 cm-1 (w) check for C-H (3300 cm-1) Hydrocarbons 3000 cm-1; 1460 and 1375 cm-1

Intensity of C=O vs C=C

1758 cm-1

1783 cm-1

1702 cm-1

1715 1686

Ligações de hidrogênio Massa atômica (C-X) Conjugação Ligações de hidrogênio Números de onda menores C-H 3000 C-C 1200 C-O 1100 C-Cl 750 C-Br 600 C-I 500

An Amine IR Spectrum => Chapter 12

An Amide IR Spectrum => Chapter 12

Summary of IR Absorptions